This application claims priority of International Application German Application No. 100 62 528.2, filed Dec. 13, 2000, the complete disclosure of which is hereby incorporated by reference.
a) Field of the Invention
The invention is directed to an arrangement for detecting impermissibly high forces acting upon the supporting structure of a vehicle, particularly an impact sensor for detecting ground contact of the tail of an airplane.
b) Description of the Related Art
The problem of impermissibly high forces acting on a supporting structure and accordingly a plastic deformation that can result in a threat to the stability of the structure is relevant in many technical fields, primarily in vehicle engineering, but especially in aeronautics.
The critical, constantly recurring moments in an airplane are takeoff from the runway, in which the length of the runway, taxiing speed, wind and the ability of the pilot play a part, and landing on the runway in which additional factors come into play (such as descent speed, approach speed and approach direction in connection with wind and other climatic phenomena combined with the flying experience of the pilot). During these processes, the tail of the airplane touches down relatively frequently. What is of concern in this respect is not so much contact with the runway as such, but that a determined magnitude of force acting on the supporting structure of the airplane fuselage is not exceeded so that a threat to the stability of the supporting airplane structure can be reliably detected or excluded. In addition, because of the great number of loads occurring on an aircraft, a tail strike indicator of the type mentioned above should allow constant checking with respect to its proper functioning so as to dependably rule out the possibility that ground contact of impermissible magnitude is not indicated due to failure of the sensor.
A conventional solution for a tail strike sensor in an airplane provides for a closed sleeve at the underside of the tail of the airplane in which two closely spaced contact lugs close the contact of a signal circuit when the sleeve is bent, so that a warning light indicates ground contact. However, in this tail strike sensor, the magnitude of the impact force and the continuous functionality of the sensor can not be detected (or can not be determined easily, i.e., without disassembling the sensor).
It is the primary object of the invention to find a novel possibility for detecting impermissibly high forces acting on the supporting structure of a vehicle which indicates possible damage to the supporting structure within a predefined impact or deformation range only in case of impermissibly high forces. Another special object is to realize a novel tail strike sensor for airplanes which permits a more reliable detection of ground contact of the tail of an aircraft. Further, it should be easier to check the functionality of the sensor.
According to the invention, these objects are met in an arrangement for detecting impermissibly high forces acting on the supporting structure of vehicles with a substantially conical housing and two electrical contacts which are arranged inside the housing and which close a signal circuit indicating deformation when the housing is deformed in that the housing is deformable in a defined manner and essentially has the shape of a truncated cone, wherein a center axis joining the centers of the base surface and top surface of the truncated cone is oriented in direction of the acting force to be detected, in that there is a spike or rod with a wedge-shaped end in the interior of the housing, wherein the rod is rigidly fastened parallel to the center axis of the truncated cone to a base surface or top surface, the electrical contacts are connected with one another within a glass tube, and a circuit is kept closed, wherein the glass tube is oriented orthogonal to the direction of the rod and transverse to its wedge-shaped end, and in that when the height of the truncated cone is reduced in excess of a determined amount due to the action of an impermissibly high force the wedge-shaped end of the rod and the glass tube are displaceable relative to one another to the extent that the glass tube is broken and the contacts are disconnected.
In particular for impact sensors with force acting in different possible directions, the top surface of the housing is curved. It is advantageous that the housing is a truncated cone with a substantially elliptical base surface and top surface in order to achieve greater stability in a preferred movement direction of the vehicle.
For aircraft and watercraft, the housing is advisably shaped as an oblique truncated cone with a rounded top surface which is inclined in the principal movement direction of the vehicle, resulting in a kind of fin shape which is aerodynamically advantageous and very stable at the same time.
The defined deformability of the housing having the shape of a truncated cone is achieved in that the permissible force acting without deformation of the housing is calculated by stability calculation by means of the finite elements method.
For reliable disconnection of the contact bridge in the glass tube in case of any housing deformation (e.g., with proportional shear deformation), a tubular sleeve is provided, into which the rod penetrates by its wedge-shaped end in an initial position (without deformation of the housing), wherein the sleeve is rigidly fastened to the base surface or top surface located opposite to the rod fastening and has a holder for the glass tube such that the center axes of the glass tube and the sleeve intersect one another orthogonally.
In an advantageous variant, the rod is rigidly fastened to the base surface of the truncated housing and the sleeve is rigidly fastened to the top surface of the truncated housing.
The housing is advisably completely filled with solid material in order to minimize any functional interference within the housing due to condensation water or external shocks or shaking without deformation of the housing. In this respect, it is advantageous that most of the housing facing the acting force to be detected is filled with a rubber-like substance, preferably silicon rubber, and the rest of the housing is completely foamed with a suitable expanding material.
A glass fuse is advantageously suitable as the glass tube forming the carrier for the contact bridge of the monitoring circuit. Another possibility for the contact-making glass tube is a double-ended light bulb. It has turned out to be particularly advantageous to use a cutoff switch type reed contact for the contact-making glass tube. This can advisably be achieved by means of a reed contact which is kept closed by providing a permanent magnet.
To enable continuous checking of the functionality of the impact sensor, the reed contact can be switched off by means of an accompanying electromagnet for checking functionality. If needed, another simple monitoring possibility advisably consists in switching off the reed contact by means of a permanent magnet which is positioned at the housing for checking functionality from the outside.
In problem cases where the impact sensor is also exposed to the risk of abrasion in addition to the impact effect (such as when an airplane grazes the runway at high speed), it is advisable to arrange a wire loop at the guide construction (sleeve) provided for the rod along the longitudinal dimension of the guide construction for detecting abrasion of the top surface of the housing, wherein the wire loop, shaped like a turning bend, is securely fastened to the top surface at a predetermined distance from the fastening point of the sleeve and is guided back in the opposite direction. In case of abrasion of the top surface of the housing, when the sleeve which is fastened therein is abraded down to the turning bend, the contact loop is accordingly interrupted and ensures that ground contact is indicated even without deformation of the housing in that a monitoring circuit is interrupted.
A wire loop of the kind mentioned above for detecting abrasion can preferably also be a connection line to a connection terminal of the contact-making glass tube which, in the same way, interrupts the same monitoring circuit as the glass tube. For secure fastening of the turning bend formed by the wire loop, this turning bend is advantageously guided through the jacket surface of the sleeve and sealed. The contact loop can optionally be guided outside the sleeve toward the turning bend and back inside the sleeve, or the turning bend is guided through to the other outer side of the sleeve.
The basic idea of the invention is based on the consideration that in impact sensors which have been used in airplanes up to the present time and which provide (one-time) indication of ground contact of the tail precisely when two electrical contacts are closed or opened by destruction of a surrounding rod, it is not possible after such an event to determine (without additional costly steps) whether the supporting structure of the airplane tail has sustained damage or not. Further, a conventional tail strike sensor can not be checked for functionality at regular (e.g., prescribed pre-flight) routine inspections. These problems are solved according to the invention with a housing which is deformable in a defined manner and a contact bridge which can be reliably destroyed when a force is exceeded. Said housing deforms only when there occurs an impermissibly strong shock (e.g., ground contact of the tail of the airplane) and, due to a reduction in its height (crumple or shear deformation), the contact bridge is destroyed by a rod and a monitoring circuit is interrupted. For this purpose, the housing comprises a material that is softer than the actual vehicle structure and is dimensioned by the finite elements method in such a way that it does not deform until after a determined force is reached. A threshold behavior of this kind in an impact sensor during collision is also important for any vehicle outside the aeronautics industry.
Through the use of a reed contact as a contact bridge protected within a glass tube, the impact sensor can be monitored for functionality at any time (cutoff function) in that it can be checked (opened) by applying an external magnetic field. In this way, it can be determined whether or not the impact sensor is still intact also when a slight (possibly visible) impact contact has occurred which has not led to a (sufficient) deformation of the housing.
By means of an arrangement of this kind according to the invention, it is possible to reliably indicate that a predetermined (impact) force on a supporting structure of a vehicle has been exceeded and at the same time to ensure the functionality of the arrangement when the permissible force has not been exceeded. An arrangement of this type which is outfitted with a reed contact can be used particularly at the tail of airplanes (as a tail strike indicator TSI) because, in addition to the fact that it can be continuously checked (e.g., during routine inspections before takeoff), it also allows a decision to be made after the occurrence of ground contact of the airplane tail as to whether ground contact has occurred without damage to the airplane structure.
The invention will be described more fully in the following with reference to an embodiment example.